Calcium is a ubiquitous second messenger involved in many cellular processes, including regulation of transcription, metabolism, proliferation, muscle contraction, and cell death both via apoptosis and necrosis.
Due to the many effects of calcium, the intracellular calcium concentration is tightly regulated, and the effects of calcium are dependent on time, place, amplitude, frequency, and duration of the calcium signal. Cellular uptake of calcium can be facilitated by electroporation, where cells are exposed to an electric field exceeding the dielectric strength of the cell membrane, resulting in generation of reversible permeabilisation structures in the membrane. This allows flux of normally non-permeating ions and molecules across the membrane.
In eukaryotic cells the concentration of free intracellular calcium is very low (10−7M), in striking contrast to the concentration of free calcium in plasma (10−3M). Thus, even a small increase in the permeability of the membrane may increase the concentration of free intracellular calcium drastically. Increase in intracellular calcium concentration due to electroporation has previously been shown, but its use in cancer treatment has not been fully investigated.
Electroporation has been used for local treatment of malignant tumors in combination with chemotherapeutic agents (electrochemotherapy) or plasmids (gene electrotransfer) in clinical trials. The cytotoxic agents bleomycin or cisplatin have been used, either by intravenous or intratumoral route, followed by application of electric pulses to the tumor. Standard operating procedures of electrochemotherapy using chemotherapeutics have been known for a few years, best illustrated by Mir et al. [2006].
Mashiba et al [2005] discloses a repetitive combination therapy that use 2% calcium chloride in combination with electroporation to induce apoptosis in human cancer cells. Intralesional injection of calcium chloride (2%, 0.1 ml) and subsequent electroporation of mice bearing the methA murine tumor cell is also disclosed. Mashiba et al [2005] is silent about any required treatment regime to the dosage of the volume required in order to avoid side effects in the surrounding tissues and particularly it is not clear from Mashiba et al [2005] what the volume of the tumors is.
Hence, an improved method for treating cancer would be advantageous, in particular a more efficient method with less side effects would be preferable.